d = int(input())
c = ["x"] * d
c += list(input())
c += list(input())
c += ["x"] * d
l = len(c)
cc = [c[:] for j in range(15 + d)]
cnt = 0
ans = 0
num = []

for j in range(15 + d):
    flag = 0
    for k in range(j,j + d):
        if cc[j][k] == "o":
            flag = 1
            break
        cc[j][k] = "o"
    if flag == 0:
        num.append(j)

for j in num:
    for i in range(l):
        if cc[j][i] == "o":
            cnt += 1
        ans = max(ans, cnt)
        if cc[j][i] == "x":
            cnt = 0

print(ans)